séminaire du lundi 16 avril 2012 à 10H30

IMPMC, Université P. et M. Curie, 4, Place Jussieu, 75005 Paris

Salle de Conférence, 4ème étage, Tour 22-23, Salle 401

MAGNETIC BLUE PHASE IN ITINERANT CHIRAL MAGNET MNSI

Daniel LAMAGO (Institut für Festkörperphysik, KIT, D-76021 Karlsruhe, Germany
Laboratoire Léon Brillouin, CEA Saclay, F-91191 Gif sur Yvette, France)

Résumé :

In MnSi with the cubic crystal structure B20, the lack of inversion symmetry induces
a chiral Dzyaloshinsky-Moriya interaction between magnetic moments. It locally
favors helical magnetic order. In addition to a long-range helical order with the welldefined propagation vector, other locally helical phases such as skyrmions and
partial order appear in its phase diagram. These enigmatic phases are suspected to
be behind many unusual properties of MnSi. I will report results of model
calculations, which show that such phases should arise naturally as a result of the
basic Dyaloshinsky-Moriya Hamiltonian. Specifically, in the absence of an applied
magnetic field, the free energy in MnSi should be minimized by the magnetic
analogue of blue phases, which have previously been observed in chiral liquid
crystals. This result is consistent with our recent neutron scattering measurements
as well as those of others. The properties of this blue phase explain a number of
previously reported puzzling features of MnSi such as partial magnetic order and a
two-component specific-heat as well as, possibly, non-Fermi-liquid resistivity at high
pressure.